The present invention relates to a controller of an area sensor having a plurality of optical channels (or paths) provided within a detection area, each optical channel defined by a set of a light emitting device and a light-receiving device. In particular, the invention relates to a controller for use with a plurality of such area sensors.
An area sensor is a kind of switch that comprises a light projector having light emitting devices and a light receiver having light-receiving devices, a set of one light emitting device and one light-receiving device forming an optical channel. If any one of the optical channels is interrupted by a moving object, the area sensor turns on. Working as a switch, the area sensor ensures the safety of the operators of machine tools, punching machines, press machines, brakes, molding machines, automatically controlled machines, coiling machines, robots, casting machines and so forth. In the case of a press machine, the area sensor is positioned in a detection area which is the dangerous zone of the machine and when fingers or any other part of the operator's body enters the detection area and interrupts a particular optical channel, the sensor detects that phenomenon and takes an immediate protective action by shutting down the machine or issuing a warning signal.
The area sensor is also used in an automatic production line at plant, where it detects the presence or absence of a moving article and signals for a transfer to the next step upon detecting the article. In this case, the area sensor works as a sensor for automatic control.
An area sensor of the type is shown in FIG. 9 and it comprises a light projector 2 in which a plurality of light emitting devices 21 such as light-emitting diodes (LEDs) that emit infrared or other radiations are aligned in a specified pitch (in FIG. 9, eight light emitting devices are provided), a light receiver 3 in which a corresponding number of light-receiving devices 31 such as photodiodes 31 that are aligned in a specified pitch in correspondence with the light emitting devices 21 so that they receive infrared beams on optical paths 9 emitted from the light emitting devices 21 in the light projector 2, and a controller 4 that controls both the light projector 2 and the light receiver 3 via cables 7. The light projector 2 and the light receiver 3 are provided in a face-to-face relationship such that the projector 2 is positioned on one side of the detection area where the operator of a press machine or the like must be protected whereas the receiver 3 is positioned on the other side of the detection area. Optical beams issued from the light emitting devices in the light projector 2 travel to the corresponding light-receiving devices in the light receiver 3 and the interruption of any one optical beam is detected. The light receiver 3 is also equipped with an indicator 6 that signals the operating status of the sensor. If desired, the indicator may be provided on the light projector 2 rather than the light receiver 3.
In accordance with the control by the controller 4, the light emitting devices 21 in the light projector 2 emit cyclically in sequence (e.g. from down to up) and with synchronism being ensured between a particular light emitting device 21 and the corresponding light-receiving device 31 in the light receiver 3, only the corresponding light-receiving device 31 is rendered to be capable of light reception whereas the other light-receiving devices 31 are incapable of light reception. The reason for ensuring that only one corresponding light-receiving device 31 at a time is rendered to be capable of light reception is that the light from a particular light emitting device 21 is not necessarily launched into the corresponding light-receiving device 31 and there may be a case in which the same light is also launched into nearby light-receiving devices 31 as light of a comparatively high intensity. In other words, the conventional area sensor is of such a design that the light reception signals from all light-receiving devices 31 are collectively fed into a single binarizing circuit and, although a particular channel is interrupted by an object that has entered the detection area, the light launched into nearby light-receiving devices 31 causes the overall signal level to exceed a threshold and the sensor will erroneously determine that the projected light is being received by the fight receiver and thus fails to achieve correct detection of the object that has entered the detection area.
On the other hand, if detection is continued with only one optical path being cyclically rendered effective at a time, the entrance of an object or fingers or some other part of the human body into the detection area interrupts the optical path 9 in the affected position so that it is no longer received by the corresponding light-receiving device 31, whereupon the sensor issues a warning signal or shuts down the machine to ensure safety for the operator.
FIG. 8 is a block diagram for the area sensor under consideration. The area sensor 1 provides with the light projector 2, the light receiver 3 and the controller 4.
The light projector 2 comprises a desired number N of light emitting devices 21 (211, 212, 21N) in the form of light-emitting diodes or the like that are spaced on a desired pitch, say, 40 mm, N light emitting circuits 22 (221, 222, . . . 22N) for driving these light emitting devices 21, a gate array 23 that scan controls the N light emitting circuits 22 on a time-sharing basis to perform the necessary processing for detecting abnormalities and displaying the detected abnormality, a clocking oscillator circuit 25 and a power supply circuit 26. In the illustrated case, the operation of the light emitting circuits 22 is controlled by using the gate array 23. Needless to say, the gate array may be replaced by other control devices such as a CPU.
The light receiver 3 comprises a desired number N of light-receiving devices 31 (311, 312, . . . 31N) in the form of phototransistors or the like that are arranged on the same pitch as the light emitting devices 21 in the light projector 2, N light-receiving circuit 32 (321, 322, . . . 32N) for performing I-V conversion on the light reception signals from the respective light-receiving devices 31, a gate array 33 that scan controls the N light-receiving circuits 32 on a time-sharing basis in synchronism with the corresponding light emitting devices 21, an indicator circuit 34 that displays the status of the associated area sensor, a clocking oscillator circuit 35, a power supply circuit 36, a light reception signal processing circuit 37 that collectively amplifies, binarizes and detects the light reception signals from the light-receiving circuits 32, a detection signal output circuit, and an output circuit 38 for delivering sync signals. Besides synchronous scan control, the gate array 33 performs auxiliary detecting operations, abnormality detecting operations and processing for displaying the results of detection. As in the case of the gate array 23, the gate array 33 may of course be replaced by other control devices such as a CPU.
The controller 4 includes a control circuit 41 in the form of a gate array; the control circuit 41 receives an external input from an external input circuit using an input terminal, a mode setting from a mode setting circuit using a DIP switch, and a signal indicative of the status of light projection from a sensor connector 42 to the light projector via a light projection status signal input circuit; the control circuit 41 also receives the aforementioned detection output and a system sync signal from a sensor connector 43 to the light receiver via a detection signal input circuit and a sync signal input circuit, respectively. The control circuit 41 delivers the following three signals from an output circuit 47: a sync signal, a mode setting signal and a shutdown output signal that are respectively sent to the light projector 2, the light receiver 3 and the press machine or the like. In addition, the control circuit 41 causes an indicator LED to be lit for indicating via an indicator circuit 48 that the controller 4 is in operation and it receives from a key switch a signal for disengaging the controller 4 from a locked-out state. The controller 4 also includes a system power supply circuit 49 for supplying operating energy to the light projector, the light receiver and the controller, an internal power supply circuit 46 with which the voltage from the system power supply circuit 49 in converted to a constant operating voltage for the control circuit, and an oscillator circuit 45 for clocking the controller.
The above-described circuit configurations of the light projector, light receiver and the controller are just one example and other configurations may be employed; for example, the circuits in the controller 4 may optionally be transferred to the light projector 2 or the light receiver 3; conversely, the circuits in the light projector 2 or the light receiver 3 may be transferred to the controller 4. Thus, the individual circuits of interest are by no means limited to those shown in FIG. 8.
The foregoing description applies to the case where only one area sensor is employed. If more than one area need be detected, a corresponding number of such area sensors are necessary. FIG. 5 shows a conventional controller circuit configuration that is employed with more than one area sensor.
In the case shown in FIG. 5, two area sensors 1 and 1A are employed. The area sensor 1 includes a light projector 1, a light receiver 3 and a master controller 4 that have the same circuit configurations as the light projector 2, the light receiver 3 and the controller 4 that are shown in FIG. 8. Similarly, the area sensor 1A has a light projector 2A, a light receiver 3A and a master controller 4 that also have the same circuit configurations as shown in FIG. 8. Thus, the two master controllers 4 each have a detecting portion and an output circuit and as a system they are independent of each other. Such master controllers are used in parallel.
A problem with the design shown in FIG. 5 is that it requires signal processing for ensuring that more than one output can be handled in one line but then the number of wiring steps increases. As another problem, the number of power supply cabling steps increases and the output portion becomes unduly redundant, thereby increasing the installation space that is unduly occupied, with the result that the apparatus becomes bulky. In addition, due to the system independency, the interruption of one optical axis in one area sensor is accompanied by the reception of the light from the other area sensor, whereupon one optical signal is interfered with by another optical signal to potentially cause an erroneous operation of the apparatus.
FIG. 6 shows another controller circuit configuration that is employed with more than one area sensor. In the case shown in FIG. 6, two area sensors 1 and 1A are employed. The area sensor 1 includes a light projector 2, a light receiver 3 and a master controller 4 that have the same circuit configurations as shown in FIG. 8, and the area sensor 1A has a light projector 2A, a light receiver 3A and a master controller 4 that also have the same circuit configurations as shown in FIG. 8. Thus, the two master controllers 4 each have a detecting portion and an output circuit and as a system they are independent of each other. Briefly, the circuit configurations shown in FIG. 6 are identical to those shown in FIG. 5, except that the two independent systems are interconnected by anti-interference lines 8 and the timings of their operations are adjusted to ensure that there will be no mutual interference between two optical signals. The circuit configuration shown in FIG. 6 eliminates the possibility of erroneous operations due to the mutual interference between two optical signals but the other problems with the circuit configuration shown in FIG. 5 still remain to be solved. That is, signal processing is required to ensure that more than one output can be handled in one line but then the number of wiring steps increases. In addition, the number of power supply cabling steps increases and the output portion becomes unduly redundant, thereby increasing the installation space that is unduly occupied, with the result that the apparatus becomes bulky.
FIG. 7 shows yet another controller circuit configuration that is employed with more than one area sensor. In the case shown in FIG. 7, two area sensors 1 and 1A are employed. The area sensor 1 has a light projector 2 and a light receiver 3 and similarly, the area sensor 1A has a light projector 2A and a light receiver 3A. The two area sensors share a common controller 4 in controlling the light projectors and receivers they use. This circuit configuration solves not only the problem of requiring signal processing for ensuring that more than one output can be handled in one line, which results in the increase in the number of wiring steps, but also the problem of increasing the number of power supply cabling steps to make the output portion unduly redundant. However, the circuit configuration shown in FIG. 7 has had a serious drawback in that if there is a change in the facility that employs the detection system under consideration, namely, if the number of area sensors changes, the common controller has to be replaced by a different one.
Further, if the controller shown in FIG. 7 is a designed to be operable up to a maximum number of optical axes, one can use area sensors having a smaller number of optical axes but a need still exists to employ a bulky controller that can handle up to the maximum number of optical axes.